In-shoe remote telemetry gait analysis system

ABSTRACT

A gait analysis system includes a shoe insert for use in a shoe worn by a subject while walking as part of a process of collecting gait data. The insert has force-sensing sensors distributed to define a sensing aperture, and each sensor provides an electrical output signal. Processing apparatus is communicatively coupled with the sensors. The processing apparatus calculates a gait line represented by a series of points, wherein each point is calculated as a spatially-weighted average of samples of the sensor output signals over the sensing aperture. The processing apparatus includes a portable telemetry transmitter worn by the subject. The transmitter is connected to the sensors to receive the sensor output signals, and transmits a radio signal carrying the sensor information. A stationary receiver receives the sensor information in a transmission from the transmitter, and provides the sensor information to a personal computer or similar workstation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/169,759, filed Oct. 9, 1998, which is a division of U.S.patent application Ser. No. 08/780,435, filed Jan. 8, 1997, which issuedon Oct. 13, 1998 as U.S. Pat. No. 5,821,633.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

The present invention is related to the field of sensors and sensorsystems used in analyzing the gait of a patient or other subject.

There has been a dramatic increase in the incidence of foot-relatedillnesses and other maladies that manifest themselves in a person'sgait, and an attendant increase in the number of consultations withpodiatrists and other medical professionals who deal with such medicalproblems. In an increasingly common scenario, a patient who visits apodiatrist is asked a series of questions about his problem, and anexamination is performed, which typically includes observing thepatient's gait during a brief walk. Oftentimes, after a possiblytentative diagnosis is reached, an orthotic device is prescribed. Thepatient returns for an additional office visit after the orthotic ismade, and the orthotic is custom-fitted by the podiatrist. There may beone or more follow-up visits to determine whether the orthotic isachieving the desired results.

Current procedures like those described above can be excessivelytime-consuming, and tend to rely excessively on trial and error.Additionally, the patient feedback for prognosis purposes is verysubjective. Thus, there has been a need for more objective techniquesfor gait analysis in the diagnosis, treatment and prognosis of podiatricillnesses.

Recently, gait analysis systems have been deployed that bring a desiredmeasure of objectiveness to the diagnosis and treatment of podiatricillnesses. One such system utilizes a special shoe that is worn by apatient during an office visit. The footbed of the shoe contains a largenumber of small pressure sensors that generate electrical output signalsindicative of pressure in a small area surrounding the sensor. Thesesensors are connected to a rather large data collection and analyzingsystem, using a lengthy cable harness with a number of wires carryingthe sensor signals. The data analysis system is responsible forcollecting data from the sensors at a given sampling rate while thepatient takes a few steps, and then performs various signal processingon the large quantity of collected data in order to presentdiagnostically useful information to the physician using the system.

Gait analysis systems such as the one described above are considerablyexpensive, partly due to their use of numerous sensors and the attendantsize of the data collection and signal processing tasks. In addition,because the patient is “tethered” to the system by the cable harnessduring use, such systems tend to be awkward to use, and are prone tocable-related malfunction. Moreover, the tethering can interfere withthe analysis by artificially restricting the movement of the patient.Accordingly, there has been a need for improved gait analysis systems.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, a gait analysis system isdisclosed that improves upon the above-mentioned drawbacks of presentsystems. The disclosed system includes a shoe insert configured for usein a shoe to be worn by a subject while walking as part of a process ofcollecting gait data. The shoe insert has a small number offorce-sensing sensors distributed in a manner defining a sensingaperture. Each sensor provides an electrical output signal. Processingapparatus is communicatively coupled with the sensors on the shoeinsert. The processing apparatus is operative to calculate a gait linethat is represented by a series of points, wherein each point iscalculated as a spatially-weighted average of samples of the sensoroutput signals over the sensing aperture.

In one embodiment, the processing apparatus includes a portabletelemetry transmitter worn by the subject during the data collectionprocess. The transmitter is connected to the sensors to receive thesensor output signals, and transmits a radio signal carrying the sensorinformation. A stationary receiver receives the sensor information in atransmission from the transmitter, and provides the sensor informationto a personal computer or similar workstation. The use of a portabletransmitter greatly enhances the usefulness of the system, by enablingthe subject to walk in a normal manner unimpeded by electrical cables orother apparatus.

Other aspects, features, and advantages of the present invention aredisclosed in the detailed description that follows.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram of an in-shoe remote telemetry gait analysissystem in accordance with the present invention;

FIG. 2 is a plan diagram of a sensor-carrying shoe insert used in thegait analysis system of FIG. 1;

FIG. 3 is a plot of sensor output versus time in the system of FIG. 1during the period when a subject's foot contacts a walking surface; and

FIG. 4 is a plot of a mean gait line for a subject as derived fromsensor data obtained in the system of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a sensor-bearing shoe insert 10 is connected to a small,portable telemetry transmitter 12. As described in more detail below,the insert 10 has force sensors located in different positions. Eachsensor is connected to a respective one of five input channels to thetransmitter 12. The insert 10 is intended for use in a shoe 14 to beworn by a subject in order to collect gait data. A receiver 16 receivesa radio signal emanating from the transmitter that carries sensorinformation signals representing the respective output values from thesensors. The sensor information recovered by the receiver 16 is providedto a personal computer (PC) 18 or similar workstation. Such aworkstation may be located remotely over a link 17 at a centralprocessing facility 19 with results sent back over the link 17.

During use of the gait analysis system of FIG. 1, a patient or othersubject dons the shoe 14, attaches the transmitter 12 to his or herclothing (for example by clipping the transmitter 12 to a belt), andwalks on a firm surface. The transmitter 12 receives output signals fromthe sensors indicative of the magnitude of force in areas of the insert10 about the respective sensors, converts these signals intocorresponding digital values, and transmits these digital values byappropriately modulating a radio frequency carrier. The receiver 16receives the modulated carrier, performs appropriate de-modulation torecover the digital values, and forwards the digital values to the PC 18using, for example, a serial communications link. An application programexecuting on the PC 18 makes various calculations on the sensorinformation, and presents the data to a user in graphical and otherforms.

In one embodiment, the transmitter 12 and receiver 16 are components ofa system called StrainLink™ available from MicroStrain, Inc. ofBurlington, Vt., USA. The StrainLink system can accommodate up to 5 datachannels in a so-called “pseudo differential mode” of operation. Eachdata input to the transmitter 12 is configured as a bridge in which oneelement is a force sensing resistor (FSR) used as a sensor in the insert10. The transmitter applies respective programmable gains to the inputsfrom bridges before the conversion to digital form. Physically, thetransmitter 12 in the StrainLink system occupies less than 1 cubic inchin volume.

FIG. 2 shows the insert 10 in detail. The insert 10 consists primarilyof a laminate body typically made of a polyester/foam core sandwich,although other materials and/or configurations are possible. As shown,five sensors 20 are disposed at key positions in the insert 10. In oneembodiment, the sensors 20 are force sensing resistors or FSRs. Twoelectrical leads extend from each FSR 20. One lead from each FSR 20 ischosen as a ground lead, and the various ground leads are connectedtogether as a common ground indicated as connection #6. The remainingleads are indicated as connections #1-#5. These leads are connected tothe respective inputs of the transmitter 12 of FIG. 1 in apseudo-differential bridge configuration, as discussed above. Theresistance of each disk-shaped FSR 20 varies with the magnitude of thecompressive force in the normal direction. When connected in a bridgecircuit with a suitable current source, this varying resistance createsa correspondingly varying voltage signal. This voltage signal isamplified by an amplifier within the transmitter 12, and converted to adigital form for transmission to the receiver 16 as discussed above.

FIG. 2 also shows a coordinate system superimposed on the insert 10 thatis used to identify locations. As shown, an “x” dimension extendslongitudinally from the toe to the heel, and a “y” dimension extendslaterally from the medial side (instep) to the lateral side (outstep).Based on the relative locations of the sensors 20 within this coordinatesystem, corresponding spatial weight values are used for certaincalculations on the sensor data, as described below.

The sensor data received by the PC 18 may be used in any of a variety ofways and for a variety of purposes. Gait analysis may require performingseveral different types of calculations on the data, comparing the datawith historical values for the same subject, etc. FIG. 3 and FIG. 4,discussed below, illustrate two uses of the sensor data for gaitanalysis.

FIG. 3 shows a plot of sensor output as a function of time over theduration of the contact between a subject's foot and a walking surface.The time dimension is given as both absolute values (51.8 secondsthrough 52.6 seconds) and as a percent of the entire contact phase. Thevertical dimension is pressure, reported as a voltage. During analysis,the pressure values are normalized by the patient's weight. The plotillustrates the following three phases of contact: (1) heel strike,indicated by relative maxima for the sensors located at the heel; (2)toe-off, indicated by maxima for the sensors located at the metatarsalsand hallux; and (3) mid-stance, which is the interval between heelstrike and toe-off. Additionally, the following points of diagnosticinterest are indicated:

1. Heel lift-off at about 55% through the contact phase.

Normal range is 50-65%

2. Forefoot contact at about 15%. Normal range is 16-23%.

3. Forefoot peak pressure at about 75%. Normal range is 70-80%.

Additionally, in the plot of FIG. 3 the peak for the medial metatarsalis substantially greater than the peak for the lateral metatarsal, whichis symptomatic of over-pronation. Thus it will be appreciated that agood deal of diagnostically useful information can be obtained from thesensor output signals in the gait analysis system of FIG. 1.

FIG. 4 shows a plot of a so-called “gait line”, which represents themovement of the center of force throughout the contact phase of a step.The points that constitute the gait line are each calculated fromsamples of the sensor signals. These points are calculated using spatialweighting techniques like those described in the above-referenced parentpatent and application, incorporated herein by reference. In particular,the spatial weighting for each sensor is directly related to itsrelative location on the insert 10 as shown in FIG. 2. Thus, in theillustrated embodiment, the weights are assigned as follows:

Sensor w_(x) w_(y) 1 .078 .440 2 .253 .174 3 .281 .860 4 .924 .727 5.924 .340

Each point in the gait line is then calculated as a weighted average ofthe samples of the sensor output signals. More formally, if the point onthe gait line is represented as (GL_(x), GL_(y)) and the scalar outputof the ith sensor is S_(i), then:

GL_(x)=Σ(S_(i)·W_(xi)) for all i; and

GL_(y)=Σ(S_(i)·W_(yi)) for all i.

The above represents the calculation of a first-order moment of thesensor data using uniform spatial weighting. It will be appreciated thatin alternative embodiments the calculation of higher-order moments maybe useful. Also, it is possible to employ non-uniform weighting, and toemploy more or fewer sensors to achieve different tradeoffs betweenresolution and complexity/cost.

An in-shoe remote telemetry gait analysis system has been described. Itwill be apparent to those skilled in the art that other modifications toand variations of the above-described technique are possible withoutdeparting from the inventive concepts disclosed herein. Accordingly, theinvention should be viewed as limited solely by the scope and spirit ofthe appended claims.

What is claimed is:
 1. A method for gait analysis, comprising: fitting ashoe insert in a shoe, the shoe insert having force-sensing sensorsdisposed at predetermined locations, each sensor providing a respectiveelectrical output signal; having a subject wear the shoe with insertwhile walking; obtaining samples of the electrical output signals of thesensors during the subject's walking; and from the samples of the sensoroutput signals, calculating a gait line being represented by a series ofpoints in a two-dimensional space corresponding to a sensing apertureextending across the shoe insert, each point being calculated as aspatially-weighted average of respective samples of the sensorinformation signals so as to indicate at least a first-order moment ofthe forces applied to the shoe insert by the subject during the gaitanalysis process.
 2. A method according to claim 1, further comprisinghaving the subject wear a portable telemetry unit connected to thesensors during the gait analysis process, and wherein obtaining samplesof the electrical output signals of the sensors comprises: generating aradio signal at the telemetry unit, the radio signal carrying sensorinformation signals, each sensor information signal being obtained froma corresponding one of the sensor output signals; and receiving theradio signal from the telemetry unit and generating digital datarepresentative of the sensor output signals, the digital data being usedin the calculation of the gait line.
 3. A method according to claim 1,further comprising determining, from the sensor output signals,respective times at which heel strike and toe-off occur during a phasein which the subject's foot is in contact with a walking surface, andcomparing these times with pre-determined normal ranges for heel strikeand toe-off.
 4. A method according to claim 1, further. comprisingdetermining an extent of pronation from the sensor output signals.
 5. Amethod according to claim 1, further comprising determining an extent ofsupination from the sensor output signals.
 6. A method according toclaim 1, further comprising including an orthotic in the shoe during thegait analysis process.